Homeostasis and Feedback Mechanisms

Homeostasis, Negative and Positive Feedback

• Homeostasis is maintaining a stable internal environment within acceptable limits. Examples include water balance, blood pH, body temperature, blood sugar, and reproductive cycles.
• Negative feedback loops counteract initial stimuli, restoring the body to its normal state. An example of negative feedback is shivering when cold to raise body temperature.
• Positive feedback leads to instability. It's a chain of events that intensify a change away from a steady state. This must be reversed or the stimulus removed. Examples include contractions during childbirth and hyperventilation.

Components of a Control System

• Sensory receptors: Specialized cells detecting internal or external stimuli (changes).
• Integrator: A control center (e.g., brain) that processes sensory input and decides on a response.
• Effectors: Muscles or glands that carry out the integrator's response.

Nervous System Divisions

• Central Nervous System (CNS): The brain and spinal cord. It integrates information from the peripheral nervous system and coordinates bodily responses.
• Peripheral Nervous System (PNS): Connects the CNS to the rest of the body. It comprises:
  • Somatic Nervous System (voluntary): Controls skeletal muscles. Sensory neurons transmit messages to the CNS, and motor neurons receive and send signals to muscles.
  • Autonomic Nervous System (involuntary): Controls smooth muscles, cardiac muscles, and glands. Further divided into sympathetic (fight-or-flight) and parasympathetic (rest-and-digest) systems.

Neuron Structure and Resting Membrane Potential

• Neuron: A nerve cell, the basic unit of the nervous system. It transmits electrical impulses. While depicted as simple wires, their function is actually much more complex.
• Neuron are more negatively charged inside than outside.
• Neuron anatomy:
  • Dendrites: Receive signals from other cells.
  • Cell body (soma): Processes information from dendrites. Contains the nucleus and organelles.
  • Axon: Transmits signals to other cells.
  • Axon terminal: Communicates with the next neuron or effector.
  • Myelin sheath: Insulating layer increasing signal speed.
  • Nodes of Ranvier: Gaps in the myelin sheath that allow the signal to propagate quickly.

Action Potential Generation

• Action potential: A rapid change in membrane potential.
• Steps:
  • Step 1 (Depolarization): Sodium channels open allowing Na+ influx, inside becomes positive.
  • Step 2 (Repolarization): Sodium channels close, potassium channels open, K+ efflux, inside becomes negative again. This may go into undershoot, where the membrane potential is briefly more negative than at rest.
  • Step 3 (Restoring resting potential): Na+/K+ pump restores the original ion distribution.

Action Potential Propagation

• Propagation of action potential occurs as a unidirectional wave of depolarization traveling through voltage-gated ion channels along an axon.
• Unmyelinated neurons: Action potential propagates continuously.
• Myelinated neurons: Action potential "jumps" between gaps in the myelin sheath (saltatory conduction), faster than in unmyelinated neurons.

Sodium-Potassium Pump

• The sodium-potassium pump maintains the resting membrane potential by actively pumping 3 Na+ ions out, for every 2 K+ ions pumped in.
• This creates and maintains a negative charge inside the neuron relative to the outside (-70 mV).

Nerve Impulse Transmission Between Neurons

• Details on the precise mechanism and diagram required to be provided in separate study materials.

Threshold Potential

• Threshold potential: The minimum depolarization level required to trigger an action potential (-55mV).
• If the stimulus is weak, the neurons will be not fire.
• The combined stimulus reaching the threshold is necessary to initiate an action potential.

Knee-Jerk Reflex Arc

• A reflex arc involving only three neurons (sensory, interneuron, and motor).
• Reflex arcs have fewer synapses and neurons, resulting in faster response times.
• The five steps of a knee-jerk reflex arc are:
  • 1. Stimulus detected by sensory receptor.
  • 2. Sensory neuron transmits action potential.
  • 3. Interneuron in spinal cord transfers message to motor neuron.
  • 4. Motor neuron transmits message to effector.
  • 5. Effector (muscle) contracts.

Cerebral Lobes

• Frontal Lobe: Motor control, higher cognitive function.
• Parietal Lobe: Sensory information (touch, temperature).
• Temporal Lobe: Auditory and visual input, language processing.
• Occipital Lobe: Visual processing.

Brain Structures

• Cerebellum: Coordinates movement.
• Medulla Oblongata: Autonomic functions (breathing, heart rate).
• Pons: Relay station between brain regions.
• Corpus Callosum: Connects the cerebral hemispheres.

Teenage Brain vs. Adult Brain

• Frontal lobe development continues in adolescence.
• Other brain regions also mature during adolescence

Endocrine System

• Endocrine system components: Glands, specialized cells (producing hormones), and a transport mechanism (bloodstream).
• Functions: Regulate body functions through hormone signaling.

Hormone Action (Steroid vs. Protein)

• Steroid hormones: Lipid-soluble, enter target cells and directly affect gene activity.
• Protein hormones: Water-soluble, bind to cell membrane receptors, triggering second messenger systems.

Pituitary Gland

• Pituitary (master gland): Regulates hormone secretions in other endocrine organs. It is controlled by the hypothalamus.
  • Anterior pituitary: Produces several tropic hormones that stimulate other glands.
  • Posterior pituitary: Stores and releases hormones produced by the hypothalamus.

Glands and Hormones

• Lists of glands and their respective hormones and functions need more specific details to be effective study aids.

Blood Sugar Regulation

• Pancreatic islets (alpha, beta, delta cells) produce hormones to regulate blood glucose.
• Glucagon: Raises blood glucose (glycogenolysis).
• Insulin: Lowers blood glucose (glucose uptake).
• Somatostatin: Regulates both glucagon and insulin.
• Negative feedback loop maintains blood glucose levels. (at 0.9mg/ml)

Kidney Function

• Kidneys remove waste products. They aid in filtration, reabsorption, and secretion of various molecules to maintain homeostasis.

Nephron Function

• Filtration: High-pressure blood filtration in the glomerulus.
• Reabsorption: Returns essential substances from the filtrate to blood, done actively and passively.
• Secretion: Eliminates additional waste products from blood into the filtrate.

Blood vs. Urine Solute Concentration

• Urine composition varies to help maintain homeostasis.
• Solute concentrations in urine will change depending on dietary intake or the body's need for them in the blood.

Blood Osmotic Pressure Regulation

• Osmoreceptors in the hypothalamus detect blood osmotic pressure.
• Increased osmotic pressure triggers ADH release, increasing water reabsorption and reducing urine production.

Hypertonic and Hypotonic Solutions

• Hypertonic: has greater solute concentration than the cell; water leaves the cell, causing it to shrivel.
• Hypotonic: has lower solute concentration than the cell; water enters the cell, causing it to swell.

Ovarian Cycle Hormones (Diagram)

• A full diagram is not possible in this format. Specific hormones and their roles in the ovarian cycle need to be listed